This invention relates to novel solder compositions or solder creams, and is particularly concerned with the provision of solder compositions especially adapted for testing high density multilayer thick film circuits and high density printed circuit boards, and to a novel system or assembly for testing such circuits utilizing such solder compositions.
Complex high density electronic circuits require testing before electronic components are incorporated into such circuits. These are called bare board circuits. Such circuits can be multilayer circuits comprising layers of conductors terminating at a point on which electronic components are to be placed. To make certain that proper electrical connections exist to each of these points, a testing system termed "bare board testing" is presently in use. In this method, holes are drilled in a circuit pattern on a test head, which is a mirror image of the pattern of the circuit to be tested, and spring loaded probes or contacts which resemble nails are positioned in the holes. Each of such nails makes contact with a connector in the test head circuit which in turn connects to a computer. This test head is known in the practice as a "bed of nails."
The "bed of nails" test head is then placed over the circuit to be tested, with each of the nails or probes on the test head in contact with each of the corresponding points of the circuit being tested on the board.
Each circuit configuration to be tested requires a different test head assembly corresponding to such circuit configuration and the cost of preparing these "bed of nails" test heads for each circuit configuration is very high.
It is accordingly one object of the present invention to provide a system for testing electronic circuits before placing electronic components thereon to ensure that all of the electrical interconnections are properly in place.
Another object is the testing of high density electronic circuits while avoiding the use of spring loaded probes or "the bed of nails" test heads presently employed in the prior art.
A further object of the invention is the provision of a novel solder composition for use in conjunction with a circuit pattern on a test head and wherein the solder composition is designed to provide the contact points between the test points of the electrical connections on the test head and the test points of the electrical connections of the corresponding circuit under test.
Yet another object of the invention is to provide a novel test head arrangement for testing high density circuits for continuity and isolation prior to assembly thereof.